1. Field of the Invention
This invention relates to a process for the preparation of an aminoacetaldehyde acetal of the formula ##STR3## wherein
R is an alkyl radical of 1 to 4 carbon atoms by hydrogenation of the corresponding dialkoxyacetonitrile with hydrogen under an elevated pressure and at a temperature of 50.degree.-180.degree. C., preferably in the presence of a catalyst and preferably in the presence of ammonia.
2. Discussion of the Prior Art
It is known that aminoacetaldehyde acetals can be prepared by the reaction of halogen acetaldehyde acetals with ammonia.
According to Org. Synth. III, p. 50, aminoacetaldehyde diethyl acetal can be obtained by the reaction of chloracetaldehyde diethyl acetal and ammonia. It is disadvantageous in this process in that it is necessary to operate with a 72-fold molar excess of anhydrous ammonia. If an insufficient amount of excess ammonia is present, two molecules of halogen acetal react with ammonia to form iminodiacetaldehyde acetal. In this reaction, one mole of ammonium chloride is produced as a solid product for each mole of halogen acetal put in. In Houben-Weyl's "Methoden der Org. Chemie", Vol. VII/1, p. 381, an example is given in which 70 wt.-% of aminoacetaldehyde diethyl acetal is obtained together with 15 wt.-% of iminodiacetaldehyde diethylacetal from chloracetaldehyde acetal.
Another method of preparing aminoacetaldehyde acetals is the reaction of halogen acetaldehyde acetals with benzylamine to form benzylaminoacetaldehyde acetals and their cleavage by hydrogenation to form aminoacetaldehyde acetals and toluene. In the first stage of the reaction it is best to operate in the presence of a relatively great excess of benzylamine. The benzylamine serves also as the reaction medium and binds the halogen hydride formed in the condensation reaction. (Cf. Bristow et al., J. Chem. Soc. 1954, pp. 616-629). This known process is very difficult. Since it would not be economical to discard the benzylaminohydrochloride, an additional procedure must be used in which benzylamine is released again by a fairly strong base, such as sodium methylate for example. In this case sodium chloride precipitates and must be removed from the reaction solution by filtration or centrifugation.
Both in the first-named process and in the second, salts are produced which contain organic impurities. Before any further use, they have to be purified. A purification procedure, however, is too expensive. For environmental reasons, the contaminated salts cannot simply be discarded. Getting rid of them without polluting the environment is a difficult problem.
Accordingly, it is an object of this invention to provide a simple process for the production of an aminoacetaldehyde acetal wherein salts contaminated with organic impurities are not produced. Moreover, it is an object of this invention to provide a process for the production of an aminoacetaldehyde dimethyl acetal wherein a large excess of ammonia is not required. Especially, it is an object of this invention to provide a process for the production of an aminoacetaldehyde acetal wherein difficult to remove pollutants are not synthesized as a result of the process and the desired reaction product can readily be obtained from the reaction mixture. Especially, it is an object of this invention to provide a method for the preparation of aminoacetaldehyde acetals with the formula given above by non-polluting reactions, i.e., with reactions in which no waste products are produced whose elimination is both necessary and uneconomical.